R1-Fe(Co)—B-A-X-M based rare earth sintered magnets with Nd2Fe14B type compound as a main phase are widely applied to various fields of electronics, automobile, computer, energy, machinery, medical apparatus and the like. When the sintered magnets are used in various devices, such as electric machinery, in order to adapt to the service conditions at a high temperature, it is required that the magnets have a good temperature tolerance and a low temperature coefficient, and the magnets should have low decay amplitudes of remanence and coercive force at a high temperature. In a conventional process, presently, heavy rare earth metals are added during smelt to increase the coercive force of magnets. However, the replacement of medium and heavy rare earth metals happens not only near the interface of main phase grains, but also inside the grains, thereby leading to an unavoidable loss of remanence. Moreover, in order to achieve the same performance, more medium and heavy rare earth metals are required in a conventional process. With respect to the scarcity of the medium and heavy rare earth resources and their increasing prices, new requirements are proposed that the coercive force can be significantly increased while the remanence decrease of the R1-Fe(Co)—B-A-X-M based permanent magnet material can be efficiently inhibited, and the cost of raw materials can be dramatically decreased. In addition, in order to improve the temperature characteristics of R1-Fe(Co)—B-A-X-M based rare earth sintered magnets so that the decay amplitude of a coercive force is smaller at a high temperature, the decay amplitude of a coercive force of the magnets at a high temperature can be well decreased by infiltrating Terbium (Tb), Dysprosium (Dy), Holmium (Ho) and Gadolinium (Gd) into the grain boundary phase of the magnets.
In accordance to above reasons, there is a need to develop a novel process which can decrease the usage of medium and heavy rare earth metals to save the cost of raw materials while improve a temperature coefficient of magnets, so that to accommodate the special requirement that the magnets used for electric motor for new energy vehicles should be sufficiently resistant against demagnetization, and to accommodate the current situation that the price of raw materials increases, particularly, the medium and heavy rare earth metals are scarce, and to overcome the defect of conventional processes that increasing the coercive force of magnets, only by adding medium and heavy rare earth metals, to satisfy the requirement to temperature tolerance of the magnets.
CN101845637A discloses a processing technology of modifying sintered neodymium-iron-boron magnet alloy, which is as follows: solving a powder of heavy rare earth oxide or fluoride into an acid solvent, soaking the magnet, taking out and drying the magnet, and placing the magnet in an argon furnace to carry out thermal diffusion treatment and then carry out annealing treatment. CN102181820A discloses a method for enhancing the coercive force of a neodymium-iron-boron magnet material, which comprises the following steps: firstly, preparing a mixed liquid of rare earth fluoride powder and absolute alcohol; secondly, coating the mixed liquor on the surface of the neodymium-iron-boron material; thirdly, placing the neodymium-iron-boron material, of which the surface is coated with the mixed liquid, in a vacuum heating furnace, and carrying out permeation treatment; and finally, tempering. The above methods still cannot well increase coercive force of magnets, and the waste of raw materials is serious.
CN104134528A discloses a method for improving the magnetic property of sintered neodymium-iron-boron flaky magnets which is: first, suspension liquid containing heavy rare earth elements and having the viscosity of 0.1 to 500 mPa·s at normal temperature and pressure is sprayed onto the surface of a sintered neodymium-iron-boron flaky magnet uniformly; second, the sintered neodymium-iron-boron flaky magnet is dried, and then a coating containing heavy rare earth elements is obtained on the surface of the sintered neodymium-iron-boron flaky magnet; finally, the diffusion treatment and the aging treatment are carried out on the dried neodymium-iron-boron flaky magnet in the environment of inert gas. CN1898757A discloses a method for producing rare earth permanent magnet material, in which a powder comprising one or more components selected from an oxide of R2, a fluoride of R3, and an oxyfluoride of R4 is present in a magnet-surrounding space within a distance of 1 mm from the surface of the magnet. However, the above documents do not disclose or imply that atomizing the mixture solution containing medium and heavy rare earth elements before being sprayed on the surface of the magnet, and thus, the medium and heavy rare earth cannot sufficiently utilized.
CN101707107A discloses a method for producing rare earth permanent magnet material with high remanence and high coercive force, in which burying a magnet in the mixed powder to carry out the infiltration. However, the infiltration effect of this producing method is relatively bad, and the waste of medium and heavy rare earth compound is serious.